The present invention relates generally to a positive displacement fluid pump and more specifically to a gerotor pump assembly suitable for use in hydraulic systems.
In a positive displacement fluid pump commonly referred to as a gerotor pump, a ring gear and a pinion gear inside of the ring gear are supported in a pump housing for rotation about parallel, laterally separated centerlines. The teeth on the respective gears cooperate to define a plurality of variable volume pumping chambers whereupon during rotation of the gear members, a pumping chamber increases in volume to a maximum volume and then decreases in volume. Fluid from the relatively low pressure inlet port of the pump is drawn into pumping chambers that are increasing in volume. Upon further rotation of the gerotor when the pumping chambers are decreasing in volume, the fluid is pushed out through the outlet port of the pump at a relatively higher pressure. The inlet and the outlet ports are separated angularly or xe2x80x9ctimedxe2x80x9d to prevent the pump chambers from simultaneously overlapping both the inlet port and the outlet port.
A common limitation exhibited by many gerotor pumps is excessive noise caused by cavitation (the rapid formation and collapse of bubbles in the pumped fluid). Cavitation in gerotor pumps is generally caused by the pump speed being greater than the time required to fill the pumping chambers. The incomplete charge of the pumping chambers entraps air or other vapor within the fluid. If not accounted for, the entrapped vapor bubbles collapse in the discharge port creating noise inducing pressure pulses that also decrease pump efficiency. The present invention provides a pump assembly with improved charging and timing conditions to reduce cavitation and resulting noise.
The present invention provides a new and improved positive displacement pump assembly with improved timing, porting geometry and inlet fluid mechanics to improve fill and reduce cavitation.
In accordance with an embodiment of the present invention, a pump assembly is provided that includes a gerotor pump and a manifold. An aspirating member is positioned between an inlet cavity in the manifold and a fluid reservoir proximate the pump assembly. High pressure fluid diverted by a flow control valve accelerates as it passes between the aspirating member and the manifold. The resulting lower static pressure draws the fluid out of the reservoir where it mixes with the relatively higher velocity diverted fluid. As the combined fluid is slowed, the static pressure increases to xe2x80x9csuperchargexe2x80x9d the inlet cavity resulting in an improvement in the inlet fill and a reduction in cavitation.
In accordance with another embodiment of this invention, a gerotor pump is provided with a plurality of pump chambers defined by the teeth of a ring gear and a pinion gear. The pumping chambers expand in an inlet half of a crescent-shaped cavity created between the ring gear and the pinion gear and collapse in a discharge half of the crescent-shaped cavity. An inlet port in a planar member faces the inlet half of the crescent-shaped cavity. A discharge port in the planar member faces the discharge half of the crescent-shaped cavity and is timed relative to the inlet port for pumping the fluid. The timing and geometry of the input port and output port are optimized to prevent noise inducing pressure spikes while maintaining sufficient back pressure in the pump chambers to collapse entrapped vapor bubbles in the fluid.
Various additional aspects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.